1. Field of the Invention
The present invention relates to a fuse for protecting components connected to an electric circuit against burning that may occur when abnormal overcurrent flows through the electric circuit.
Recently, there have been strong demands for the miniaturization of electronic apparatus. In order to meet these demands, the length of wiring of a circuit on a printed board tends to be rather small with charging sections having opposite polarities tending to be placed in close proximity to each other as well. Due to this, when compared with a case in which a conventional printed circuit board is used, a greater magnitude of abnormal current tends to flow once a short-circuit occurs.
In order to cope with this, smaller circuit protecting components also have been demanded, and the distance between terminals of such smaller circuit protecting components has been decreased. In cutting off abnormal current, there is a close relationship between the occurrence of arc discharge and the magnitude of abnormal current and/or the distance between the terminals. The greater the magnitude of abnormal current becomes, or the smaller the distance between the terminals becomes, the more easily longer arc discharge occurs. Arc discharge generates heat having a high temperature of several thousand degrees centigrade, and due to this there is a risk of the circuit protecting components themselves being burnt. Thus, cutting off the current becomes more and more difficult when trying to satisfy the demands for the miniaturization of circuit protecting components.
2. Prior Art
Conventionally, in a well known fuse of this type is well known an arc-extinguishing material is packed around a fusible element so as to extinguish a high-temperature arc that is generated after the fusible element has been fused by abnormal current.
In the fuse described above, since the arc-extinguishing material is brought into direct contact with the fusible element, the arc-extinguishing material abrades or cuts into the surface of the fusible element, whereby the fusible element is damaged. Thus, the fuse of this type has a drawback in that it mechanically breaks down due to the damage so caused. In addition, when the fusible element is fused by a great magnitude of current, the complete dispersion of metal vapors rising from the fused fusible element is prevented by the arc-extinguishing material surrounding the fusible element, preventing the creation of wide spaces between metal particles, and resulting in poor insulation. Thus, there is the risk of an arc discharge being caused again. Moreover, it is a very difficult operation to pack a particulate arc-extinguishing material into a small fuse's main body. Therefore, the productivity associated with the manufacturing process is low.